In the face of the existing HIV-1 epidemic, an effective mix of prevention modalities are needed to begin to reduce the incidence of HIV-1. This includes the used of topical microbicides. These are products that would be used to prevent the sexual transmission of HIV-1; including receptive anal intercourse. Project 1, Nonclinical Strategies for Refining Combination Rectal Formulations, of this U19 will strive to ensure that a safe and effective rectal microbicide will be developed. To date, the Phase 2b trials of